The Devil is in the details. Illinois' 3" law has "intent" written into it, which means that if you have a 5" knife with no intention to use it as a weapon, you are OK. BUT if you use ANY knife (no matter how short) as a weapon, it becomes a WEAPON, and you will have to lawyer up. Chicago has its own knife laws, and you don't even want to go there.

Missouri's 4" law has no "intent" written into it, so my long pocket knives I carry in Illinois are stowed when going through Missouri.

License to carry a pocket knife in KY? I better check that out before I travel there again.